The present invention relates to a new and improved method of, and apparatus for, manufacturing straight or inclined toothed machine elements, especially spur gears, by cold working or rolling.
Heretofore attempts to fabricate spur gears by cold rolling were principally carried out in two different ways:
According to a first technique the teeth were rolled at a rod-like blank, whereafter the individual gears were severed. What is disadvantageous with this method is the expensive pretreatment operations carried out upon the rod by grinding, something which is necessary in order to ensure for the proper guiding of the relatively long parts during rolling. Furthermore, the expensive further processing work carried out at the rolled rod by sawing and drilling as well as the loss of the rod ends, which possess too inaccurate teeth profile, had to be tolerated, with up to 70% of the blank having to be cut. Since the cutting work is inaccurate, the cut-off gear discs do not possess any exact axial contact surface for the further processing work, so that for the exact centering needed for the subsequent operations, for instance grinding of the bore, there was only available the possibility of reception in the pitch circle, for instance clamping by means of inserted roller bodies. In the case of relatively small gears this was particularly associated with extreme difficulties and rejection of the workpieces.
The second prior art technique contemplates rolling individual gears. Thus, due to axial flow of the material at the region of the teeth there is brought about a pronounced axial swelling of the material at the end surfaces of the gear. This in turn means that the teeth must be fabricated at the blank with large axial tolerances owing to the inaccuracies prevailing thereat, and which must be again cut-off following the rolling operation. With this procedure there is likewise unavailable any precise axial starting surface for the further processing operation following the rolling operation, and the procedure is uneconomical due to the cutting work.
For the reasons mentioned the rolling of individual gears has not been widely accepted in relation to the rod rolling technique. The rod rolling technique, in turn, has certain limitations concerning the economies of this process.